Place tart shells on ungreased baking sheets. In a large bowl, beat cream cheese, lemon juice and salt until smooth. Add egg; beat on low speed just until blended. Stir in tomatoes, bacon, basil and onion mixture.

Spoon 2 teaspoons filling into each tart shell. Top each with 1/2 teaspoon crushed crackers and 1/2 teaspoon cheddar cheese.